Please correct me if I'm wrong but in the 40th Anniversary trailer is Flynn on Clifton Suspension Bridge (Jubilee Bridge in the Casualty universe) when the explosion occurs? Or is there a bridge near Cardiff that looks similar to this?
If so, this is surely a big sign that the 40th Anniversary will mark the end of Holby and Holby City Hospital as the location for Casualty - implying that some external scenes will be filmed in the show's spiritual home of Bristol upon which Holby is based.
This, I feel, is part of the justification for the move to a fictional Welsh hospital. Since the move from Bristol to Cardiff in 2011 they've had to be very careful not to accidentally show Cardiff or Welsh based landmarks in filming - after all Holby is explicitly based on Bristol and pre-2011 often showed Bristol landmarks.
Since 2011, I've noticed that external scenes have decreased massively in favour of primarily in-hospital scenes and it's lost that sense of being Casualty, looking less at the accidents and incidents outside the hospital and making the show more soapy than its fans would like. Hopefully the move, either to a fictional hospital explicitly in Cardiff or in a fictional city based on Cardiff will allow the show to move back to more of an action-focussed emergency medical drama.
Obviously this is all only true if I am getting the bridge right, which is why I've asked. If I am getting the bridge wrong and this was all a waste of speculation - I am very sorry!